The present invention provides data reading devices where the emitter and detector for reading digitally encoded data from the surface of a data carrier are mounted in a single unit. By so doing, the size of the data reader may be reduced, its cost may be reduced, and its applicability to uses other than reading data from compact discs (CDs) or from printed bar codes on packages of goods sold at retail, is greatly enhanced.
The use of encoded data and decoders comprising lasers and associated control and decoding circuitry, is by now well known throughout most of the civilized world. For example, most retail stores, whether grocery stores, convenience stores, department stores, or the like, utilize bar code readers to read a unique code which may be printed on the packaging or on a label affixed to nearly any kind of goods which may be sold at retail. Such goods are, of course, packaged products of all sorts that may be sold through food markets, and stores of all descriptions, hanging and dry goods, fabrics, packaged meats, etc. In each case, a code which is unique to the specific product--either by the nature of the product, or even according to the size of the package of product which may be purchased in various sized packages--is affixed to the product. The price of the product may also be encoded, for example in packaged food stuffs which are sold by weight, and for which a specific portion in keeping with the customer's wishes has been packaged and labelled. Otherwise, the package size and product description are encoded in the bar code, and are maintained in a look-up table in a computer to which the bar code reader is attached, so that the cash register display will correctly display the size and type or brand name of the product then being scanned by the bar code reader at the cash register. In any event, the bar code reader utilizes a laser and such a device as a reflectometer, where the laser beam is swept across the bar code and the reflection from the bar code is received at the reflectometer as a series of pulses of varying strength, from which the bar code data can be decoded.
Other widespread uses of laser devices for data decoding are in compact discs, where music, pictures, printed material, animated pictures, colour data associated with pictures or animated pictures, and the like, are to be found. The usual manifestations of such devices and the discs that are utilized with them are music compact discs, CD movies, reference material on compact discs readable by a compact disc reader in a computer, computer programs on a compact disc, and so on.
However, many other purposes exist for which the digital data encoded in a data-carrying stratum of a data carrier could be decoded for a variety of purposes--many of which are security related. For example, identity badges of persons employed in high security in industry and government might carry encoded data which might replicate that person's fingerprints, facial features, voice, or any combination of them. The data badge would be inserted into a decoding station and the data that is read from the badge is compared with fresh data taken from the person by way of reading that person's fingerprint, digitizing his facial features, having him speak a predetermined phrase into a microphone, and so on, at that time. Clearly, it would be more advantageous for that data to be encoded in a security badge rather than on a disc which would have to be carried by the person.
Another widespread purpose to which a data carrying card could be used to determine information about the person carrying the card would be such as health cards used by government operated health insurance programs such as the Ontario Health Insurance Program (OHIP) operated in the province of Ontario, Canada. There, each time an individual visits a health facility of any sort, a hospital, a doctor's office, a medical laboratory, and so on, information is derived from the health card, and the health insurance program is billed by that care-giving facility for the procedure or service given to the patient. However, widespread fraud is known to occur, and that fraud could be considerably reduced by taking additional measures and encoding considerably more data concerning the person presenting the card for service. Presently, such cards are magnetically encoded; and, of course, any card having a magnetic strip on its surface can be re-encoded by any person having the right equipment to do so. If, on the other hand, the information and data were digitally encoded in such a manner that they could only be decoded using equipment such as that provided by the present invention, then fraudulent use of such cards would be essentially eliminated.
Still other uses for cards or strips of material carrying digitally encoded data are such as passports, driver's licenses, and the like.
Other purposes may include strips of material affixed to high priced goods such as camcorders, cameras, and the like. In those instances, such data as the serial number of the device could be encoded in a strip of material or label affixed to the goods, where the serial number is determined by decoding that data and could then be compared by visual inspection with the serial number stamped onto the device, by the retail clerk at the time that the device is being sold.
It is also possible, of course, that discs of the sorts discussed above, or those carrying digitized photographs or the like, might be required to be decoded in other than ideal conditions in the home, office, automobile, or the like. In those instances, such as in railway marshalling yards, hospitals or industry where very expensive or very dangerous or very poisonous substances are being handled, and so on, a small and portable device to decode data carried on a disc or other data carrier such as cards or badges as described above, might be utilized.
In all events, what the present invention provides are data reading devices that will decode data that is encoded not only in one, but also in a plurality of surfaces provided on the data carrier. If the data is encoded in a plurality of surfaces, then because the data reading device of the present invention utilizes a single wavelength laser diode, each of the surfaces must be transparent to light emitted from that single wavelength laser diode, and must be otherwise configured to work with data carriers having multiple data surfaces.
Of course, in all events, data encoded in a surface of a generally planar data-carrying stratum is encoded either as positive-going or negative-going surface irregularities in that surface, where the positive-going or negative-going sense is with respect to a predetermined datum plane.
There are a variety of manners in which the surface irregularities can be formed in the surface of a data-carrying stratum, whereby the data is laid out in a track in the form of a series of grooves or pits, or ridges. In each instance, the groove or pit has two sides, and the ridge has two sides, with respect to the scanning direction so that it can be distinguished from its datum plane in such a manner that positive-going or negative-going pulses occur. Thus, for example, each groove might be distinguished upon being scanned first by a negative-going pulse and then a positive-going pulse, and each ridge might be distinguished upon being scanned first by a positive-going pulse and then by a negative-going pulse.
The power consumption of any data reading device in keeping with the present invention may be sufficiently low that it can be extremely portable, and as such may be powered only by batteries. This may come as a consequence not only of the utilization of single wavelength laser diodes which are quite energy efficient, and the use of solid state circuits having very low power requirements, and also by providing means by which the data-carrying stratum of the data carrier may be moved relative to the data reading device, or vice versa, such as by swiping a card through the device by hand.
The present invention provides several different embodiments of data reading devices for reading digital data encoded in a surface or a plurality of surfaces of a generally planar data-carrying stratum of a data carrier, where the digital data is encoded in the surface or surfaces as either positive-going or negative-going surface irregularities, as determined with respect to a predetermined datum plane. Any of the data reading devices in keeping with the present invention will comprise at least one focusing objective lens, whereby light from a single wavelength laser diode may be focused at its single frequency. Other features of the present invention include various decoding circuits, whereby signals which are indicative of and, indeed, are essentially directly representative of the surface irregularities on any data surface, may be decoded so as to extract that digital data. However, since decoding circuits are generally well known, they are not discussed in any detail herein. On the other hand, the nature by which signals are derived that are indicative of digital data encoded in one or a plurality of data carrying surfaces, lies at the heart of the present invention.
It is recognized that the nature of digital data encoded on any digital data carrying stratum or surface is such that there is a very high packing density for such data. In essence, it has been known previously that data could be decoded if the data, which is represented by surface irregularities such as grooves, or pits, or ridges, has a significant dimension--being either the width of a groove, or pit, or ridge, or the distance of one such groove, or pit, or ridge, from another--of only a few microns. However, the present inventors have discovered that, by utilizing the present invention, much higher resolution can be obtained, whereby the significant dimension for such data may be less than one micron. Moreover, such highly packed data may also, in keeping with other aspects of the present invention, be stored in and decoded from a plurality of surfaces which are stacked one on top of another.
One of several principals upon which the present invention is based is the knowledge that certain single wavelength laser diodes, particularly such a GaAs diodes, which have no protective film or the like placed over the semiconductor or over the laser light window associated with it, will experience current anomalies of the current flowing through the diode when light from the diode is reflected back onto the semiconductor surface. What happens is that the impinging reflections on the single wavelength laser diode cause interference at the pn junction within the single wavelength laser diode, and therefore anomalies in the current flowing through the single wavelength laser diode are caused. Those anomalies occur, of course, in real time, as a consequence of whatever light may be impinging upon the semiconductor at any instant in time. An arrangement of a single wavelength laser diode, a focusing lens, and a data carrying surface can be made, whereby light that reflects off the data carrying surface will be re-transmitted to impinge on the semiconductor. Thus, the re-transmitted light reflected for the data carrying surface will be affected by the irregularities on that surface, and will therefore be a function of those irregularities and of the digital data which those irregularities represent.
Accordingly, detection of those anomalies in real time will result in a signal which can be decoded so as to obtain a signal which is directly related to the digital data, in any form which can be processed a data signal processor, computer, or like device. Thus, such digital data can be utilized in the manner for which it is intended; but in keeping with the present invention, that digital data may have a very much higher packing density and also be capable of being derived from a plurality of stacked digital data carrying surfaces.
Another surprising phenomenon upon which operation of data reading devices in keeping with the present invention is based, is that which is described in the literature as the Gugens Effect. Essentially, light waves which impinge on a hole, especially a very tiny hole, will result in a secondary propagation from that hole which is spherical. This phenomenon has been known for a long time, and is manifested in such as a camera obscura, or pinhole camera.
However, the present inventors have discovered that an objective lens can be placed in the path of the secondary spherical propagation from the pinhole, which effectively appears as a point source of light for an objective lens, and the light can be re-focused to another point. Moreover, that re-focused light can be focused with very high resolution, much greater than the resolution that can be obtained merely be focusing light impinging on the objective lens directly from a single wavelength laser diode. Accordingly, since higher resolution can be obtained, higher packing density of data can be obtained.
Still further, the present inventors have discovered that if a diaphragm which has a pinhole in it, and which is interposed between a single wavelength laser diode and an objective lens so that the pinhole in the diaphragm appears effectively as a point source of light, as described above, but the diaphragm is moved up and down in the same direction as the light is directed, in a controlled manner, that has the effect of moving the apparent point source of light up and down; and that, in turn, results in the re-focused light passing from the objective lens being focused on a point in space which also moves up and down, in concert with the up and down movement of the diaphragm.
Accordingly, it is possible to focus the light from a single wavelength laser diode on one of several different planes that are stacked one above another, if the pinhole diaphragm is moved up and down within predefined limits of movement which are sufficient to encompass the depth of the stacked data layers.
Therefore, in keeping with a first embodiment of the present invention, this invention provides a data reading device for reading digital data encoded in a surface of a generally planar data-carrying stratum of a data carrier, which comprises a single wavelength laser diode having a light output at a single frequency, and having a direct current power supply with a regulated voltage output for the single wavelength laser diode. A precision shunt is connected in series with the laser diode, across the output of the power supply, and an input to an operational amplifier is connected across the precision shunt. The output from the operational amplifier is connected to data decoding circuits.
A focusing lens having a short focal length is provided, together with a support for a data carrier which will be placed thereon. The placement of the data carrier is such that the surface of the data carrier will be in a prescribed plane.
A pinhole diaphragm having a pinhole therein is interposed between the laser diode and the focusing objective lens. The pinhole, the center of the laser diode, and the center of the focusing objective lens, are all substantially in linear alignment one with another; and the pinhole diaphragm is placed linearly away from the prescribed plane for the surface of the data carrier at a distance which is substantially equal to twice the focal length of the focusing objective lens.
Thus, when the pinhole is illuminated by the single wavelength laser diode, it will act substantially as a point source of light with respect to the focusing objective lens, and will permit light reflected from the data carrier surface back through the focusing objective lens to be re-transmitted back to, and impinge upon, the single wavelength laser diode. The single wavelength laser diode is such that reflected light at its single wavelength which impinges on the diode will cause interference at a pn junction within the single wavelength laser diode, and will thereby cause an anomaly in the current flowing through the single wavelength laser diode and through the series connected precision shunt. Variations in the reflected light will, of course, cause varying anomalies in the current.
The mounting arrangement of the laser, pinhole diaphragm, focusing objective lens, and data carrier support is such that when there is relative motion of the data carrier on the support with respect to the focusing objective lens, light from the lens is focused on the data surface. Reflections and changes in the reflections due to the irregularities in that surface are at least partially re-transmitted back through the focusing objective lens and through the pinhole, and will thus impinge on the single wavelength laser diode.
Accordingly, anomalies in the current flowing through the laser diode and the series connected precision shunt which are caused by changes in the reflections due to the data carrier surface irregularities, will occur in real time, and are manifested by variations in voltage across the precision shunt. The variations in voltage across the precision shunt are, in turn, detected by the operational amplifier, and result in a signal which is fed from the operational amplifier to the decoding circuits, which signal is a direct function of the data carrier surface irregularities, in real time. Thus, decoding of the signal from the operational amplifier by the decoding circuits results in an output from the decoding circuits of the digital data.
A further embodiment provides for mounting the pinhole diaphragm in a mounting element such as a piezoelectric ring, or like element, which is electrically connected to and excitable by a pulse generator. When the piezoelectric ring is excited by the pulse generator, the pinhole diaphragm, and therefore the pinhole, is moved upwardly and downwardly within predefined limits, with respect to the single wavelength laser diode, along an axis which is defined by the linear alignment of the laser, the pinhole, and the objective lens.
Thus, the focus point of light which is focused by the focusing objective lens will likewise move upwardly and downwardly within the same predefined limits of movement.
If, therefore, there are a plurality of data surfaces which are above one another, and at least any of the data surfaces which is above another surface is transparent to the light emitted by the single wavelength laser diode so as to permit the light to pass therethrough, then the moving focus point of light may impinge on one or another of a respective plurality of data surface planes.
The decoding circuits are also connected so as to receive an input from the pulse generator, so that digital data from the shunt element may be decoded in real time by co-relating the signal therefrom at an instant in time with pulses from the pulse generator, and determining the relative position of the focusing point of light at that instant in time. Thus, data from any of the plurality of data surfaces may be identified as being from a respective data surface, and all data from all data surfaces may be collected and utilized as discrete and identifiable data.
Yet a further embodiment of the present invention provides for the placement of a pinhole diaphragm above a first focusing objective lens, a prism, and a second focusing objective lens, all of which are in substantially linear alignment with one another, and with the prism being interposed between the first and second focusing objective lenses. The prism has an inclined surface which is placed at substantially 45.degree. orientation with respect to the central axis of the laser diode, and on that surface there is a translucent, semi-reflective layer which faces towards the second focusing objective lens. Thus, light passing from the first objective lens will pass through the incline surface towards the second objective lens, and light which passes back through the second objective lens in a direction towards the prism will be at least partially deflected by the prism in a direction perpendicular to a the central axis.
A photo-sensor surface faces the incline surface so as to receive light which is deflected from the semi-reflective layer and is connected to decoding circuits to receive signals from the photo-sensor surface which are a function of variations in the intensity of light falling on the photo-sensor surface from the inclined surface. Otherwise, when there is relative motion between the second objective lens and the data carrier, focused light on the data surface will be reflected back through the second objective lens, and irregularities in the data surface will result in irregularities in the reflected light, and thus will result in signals from the photo-sensor surface which are indicative of the irregularities in the data surface. Once again, those signals can be decoded to derive the digital data.
Still further, as above, the pinhole diaphragm can be mounted in a mounting element which can be excited by a pulse generator, so that data which are embedded on a plurality of data surfaces can be detected and decoded.